1. Field of the Invention
The present invention relates to a starter protection device for protecting a starter by preventing a continuous supply of electric power to the starter and by preventing accidental activation of the starter during inertial rotation of an engine or the starter.
2. Description of the Prior Art
Generally, a starter for starting an engine is activated by turning to a start position of a key switch, thereby igniting and starting the engine. After ignition and starting of the engine, the starter is itself stopped by turning the key switch off of the start position.
If the key switch cannot be returned from start position for some reason, and the starter continues operating even after the engine starts, the starter will be damaged by overheating.
In addition, if the engine fails to immediately ignite when the key switch is turned to the start position, and the key switch is then turned immediately both off and on the start position, then the starter will be activated as the engine or starter is still rotate, thereby damaging the ring gear of the engine or the starter.
Therefore, a starter protection device has been in use which protects the starter by detecting from the starting state of the engine through the engine speed from voltage generated by an alternator or the like.
FIG. 6 shows an arrangement of such a conventional starter protection device for a motor vehicle.
In the figure, a starter 2 is connected across a car battery 1, and mainly consists of a main switch 3 and a motor 4. The main switch 3 has coils 3a, 3b, and a contact 3c. One end of the contact 3c is connected to a positive terminal of the battery 1, while the other end is connected to a negative terminal of the battery 1 through the motor 4. The coils 3a and 3b are connected in series and are connected in parallel across the motor 4. A common connection point of the coils 3a and 3b is connected to the positive terminal of the battery 1 and a movable terminal of a key switch 6 through a contact 5b of a starter auxiliary switch 5. The key switch 6 has the following fixed terminals, an OFF terminal, an IG terminal (ON terminal), and an ST terminal, as well as a movable terminal. The movable terminal is connected to the positive terminal of the battery 1.
A starter protection device 7 protects the starter 2 by controlling the starter auxiliary switch 5, and comprises a frequency-voltage converter (hereinafter called an "F-V converter") 701 for converting the frequency of alternating current voltage generated by an alternator 8 in response to the rotation of the engine into direct current voltage, and a comparator 702 which is supplied with the output voltage of the F-V converter 701 at its inverted input terminal and compares this voltage with a predetermined value previously applied to its non-inverted input terminal. The predetermined value of the comparator 702 is established by voltage divider resistors 703 and 704. The output terminal of the comparator 702 is connected to the base of an output transistor 705.
The starter protection device 7 further comprises a power supply circuit 706 connected to the IG terminal of the key switch 6, and a timer circuit 710 which is supplied with power supply from the power supply circuit 706. The power supply the power supply circuit 706 is arranged to also supply power to the F-V converter 701 and the comparator 702. A smoothing capacitor 707 is connected to the output side of the power supply circuit 706.
The input side of the timer circuit 710 is connected to the common connection point of the main switch 3 and the auxiliary switch 5 through an inverter 708. The common connection point is grounded through a resistor 709. The output side of the timer circuit 710 is connected to the base of the output transistor 705 through an inverter 711, and the IG terminal of the key switch 6 through a resistor 712. The collector of the output transistor 705 is connected to the ST terminal of the key switch 6 through a coil 5a, of the auxiliary switch 5, and a diode 713, which are parallel connected, and its emitter is grounded. The diode 713 is a so-called fly-wheel diode for controlling surge voltage generated in the coil 5a of the auxiliary switch 5 when the output transistor 705 is turned off.
Now, the operation will be described.
When the key switch 6 is closed through the IG terminal, voltage of the battery 1 is applied to the power supply circuit 706 of the starter protection device 7, and to the base of the output transistor 705, whereby the output transistor 705 becomes conductive.
Then, when the key switch 6 is closed through the ST terminal position, current flows from the battery 1 through the coil 5a of the starter auxiliary switch 5 and the output transistor 705, thereby energizing the coil 5a of the auxiliary switch 5 to close its contact 5b. Closing the contact 5b causes electric power to be supplied to the coil 3a of the main switch 3 of the starter 2, and closes its contact 3c. Then, the voltage of the battery 1 is applied to the motor 4 of the starter 2, and the motor 4 starts rotating to start the engine (not shown).
As the engine increases its speed, the alternator 8 begins power generation. Then, the frequency of the alternating current voltage from the alternator 8, which is input to the F-V converter 701, increases as the engine speed increases, and the output of the F-V converter 701 also increases proportional to the input.
When the engine speed reaches a starter disengaging speed, the output of the F-V converter 701 exceeds a predetermined value, whereby the comparator 702 becomes conductive: that is, its output level is changed over to the low level "L."
This turns off the output transistor 705. The coil 5a of the auxiliary switch 5 is deenergized to open its contact 5b. Power supply to the main switch 3 of the starter 2 is stopped to stop the motor 4 of the starter 2, the starter 2 is disengaged from the engine to prevent continuous power supply.
On the other hand, as described above, in a series of operations for turning on the output transistor 705 by changing over the key switch 6 from the OFF terminal to the IG terminal and then to the ST terminal to rotate the motor 4 of the starter 2 and thereby start the engine, when the key switch 6 is disconnected from the ST terminal before the output transistor 705 is turned off, the key switch 6 returns to the IG terminal to deenergize the coil 5a of the starter auxiliary switch 5 and to open its contact 5b. Thus, the current is shut off from flowing through the coils 3a and 3b of the main switch 3 of the starter 2, so that the potential of the common connection point of the starter auxiliary switch 5 and the main switch 3, or the potential of the input of the inverter 708 becomes substantially the low level "L", and the input side of the timer circuit 710 is supplied with a high level input signal "H" inverted by the inverter 708.
The timer circuit 710 starts operating in synchronization with the application of input signal, and generates a high level output signal "H" at its output side for a predetermined period of time. The high level signal "H" is inverted by the inverter 711 into a low level signal "L," and supplied to the base of the output transistor 705. Therefore, even if the key switch 6 is turned to the ST terminal position again, the output transistor 705 maintains the OFF state during the predetermined period of time the timer circuit 710 operates. That is, even if the key switch 6 is turned to the ST terminal position during the predetermined period of time the timer circuit 710 continues operating after stopping power supply to the starter, no current flows through the coils 3a and 3b of the main switch 3, and the contact 3c remains open, so that the starter 2 cannot be operated. Thus, accidental activation is prevented during inertial rotation of the engine or the motor 4 of the starter 2.
However, the conventional starter protection device for detecting the starting state of the engine with the voltage generated by the alternator as described above has a problem in that it cannot be installed on an engine without an alternator.
In addition, the conventional starter protection device described above has a problem in that wiring from the alternator and the IG terminal of the key switch starter protection device is required.
The present invention is made to eliminate the problems described above, and is intended to provide a starter protection device substantially that operates only by a signal from a key switch, does not require wiring from an alternator or the like.